Radio frequency (RF) receivers are used in a wide variety of devices including, but not limited to, televisions, radios, mobile phones, pagers, global positioning system (GPS) devices, cable modems, cordless phones, door opening systems, and other devices that receive or transmit RF signals. In some examples, RF receivers may utilize frequency translation or mixing.
The majority of typical RF receivers perform frequency translation or mixing using an oscillator and an analog multiplier or mixer. An oscillator will typically output a local oscillator (LO) signal in the form of a sine wave or periodic waveform having a tuned frequency (fLO). A mixer may be configured to mix the RF input signal spectrum, which may include desired spectral content at a target channel having a particular center frequency (fCH), with the LO signal to form an output signal having spectral content at frequencies equal to the sum and difference of the two input frequencies, namely fCH+fLO and fCH−fLO. One of these components forms the channel center frequency translated to the desired IF frequency, and the other component can be filtered out.
Unfortunately, sensitive analog circuits or receiver circuits can be sensitive to interference from nearby circuitry. In particular, nearby circuitry can produce electromagnetic interference, which can be coupled into the receive channel and which can introduce noise or spurs within the channel of interest. Thus, coupling interference from nearby circuits can present a problem for monolithic integrated circuits, multiple chips in a single package, or even multiple chips on a printed circuit board.